Flexible wall surface

ABSTRACT

A reference surface, e.g. a lapping surface, is formed on one of the external faces of a hollow pressure vessel. There are elements to vary the internal volume of this vessel, and the volume is filled with fluid. When the surface wears from its true shape, the volume is adjusted so as to change the pressure acting upon the face from the inside, so as to change the contour of the reference surface and compensate for the wear.

nited States Patent [191 Pinn [451 Feb. 12, 1974 FLEXIBLE WALL SURFACE Inventor: Ernest Henry Pinn, Richmond,

England National Research Development Corporation, London, England Filed: June 19, 1972 Appl. No; 264,010

[73] Assignee:

[30] Foreign Application Priority Data June 22.1971 England ..292l4/7l US. Cl. 51/212, 51/209 DL, 51/373 Int. Cl B24d 17/00 Field of Search... 51/209 R, 209 DL, 212, 373,

References Cited UNITED STATES PATENTS 7/1971 Cameron 269/22 X 1,045,201 11/1912 Shoop 51/373 3,465,481 9/1969 Szwarcrnan.... 51/324 1,493,779 5/1924 Humphreys 51/373 Primary Examiner--Donald G. Kelly Attorney, Agent, or FirmCushrnan, Darby & Cushman [57] ABSTRACT A reference surface, e.g. a lapping surface, is formed on one of the external faces of a hollow pressure vessel. There are elements to vary the internal volume of this vessel, and the volume is filled with fluid. When the surface wears from its true shape, the volume is adjusted so as to change the pressure acting upon the face from the inside, so as to change the contour of the reference surface and compensate for the wear.

5 Claims, 2 Drawing Figures SHEET 1m 2.-

1 rLExmLE WALL SURFACE This invention relates to reference surfaces, by which we mean surfaces of accurately known shape, which may be used in the testing or production of other accurate surfaces. The invention applies in particular to lapping surfaces or laps, well known in engineering for use in the production of components that must be accurately flat and that must possess a high quality finish. At a late stage, possibly the final stage, in their production such surfaces are rubbed against a surface of softer metal, called the lapping surface, carrying a film of lubricant into which particles of a fine abrasive have been mixed. Unfortunately laps tend to wear convex or concave during use, usually the latter, and have themselves to be re-lapped frequently to rectify this wear.

The present invention aims to provide an adjustable reference surface which can go far longer between such re-shaping, since the earlier stages of wear will be counteracted by the adjustment. The invention is defined by the claims at the end of this specification, and a device according to it will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a plan view of a cylindrical pressure vessel supporting a lapping surface, and

FIG. 2 is a section on the line 11 II in FIG. 1.

A cylindrical vessel 1 with robust side wall 2 has a robust base 3 containing an inlet 4 for a filler plug 5 sealed by an O-ring seal 6. Base 3 is attached to side walls 2 by screws 7 and sealed by an O-ring seal 8. The top of the cylinder is constituted by the reference or lapping surface 9. This is shown integral with the side walls 2 but need notbe; it could for example be a separate and interchangeable unit, attached and sealed to the side walls in like manner to the base 3. Lapping surface 9 is far thinner than walls 2 and base 3 and comparatively flexible. Face 10 of the surface must be made of a material appreciably softer than the work that is to be lapped upon it, so that the particles of fine abrasive used in the lapping operation tend to embed in the surface rather than in the work. The face may indeed be presented by a thin layer mounted on, and of different material from, the rest of the surface. While the device is being made, face 10 is ground accurately to shape, but as use proceeds the exposed surface tends to become more concave, calling for corrective lapping which in effect wears down the unworn parts of the face to the depth which the worn parts have suffered. Eventually, the whole of face 10 becomes too thin for further use, and surface 9 must be replaced.

A piston-and-cylinder device 11 is held in place in a cavity in side wall 2 by screws 12 and sealed by an annular seal 13. Device 11 comprises a cylinder 14 with a screw-on end cap 15 and inner wall 16. Holes 17 through the cap allow communication between the interiors of cylinder 14 and vessel 1. A piston 18 moves within cylinder 14. Face 19 of this piston is in communication with the interior of vessel 1 by way of holes 17, and is separated from cap 15 by a compression spring 20. The piston carries a piston ring 21, andthe reverse face 22 of the piston abuts a rod 23, threaded at 24 to engage with corresponding threads at 25 in the bodyof cylinder 14. Rod 23 alsocarries a snob 26; by turning this piston 18 can be moved' up and down the bore of cylinder 14. v

Before the maker attaches the base 3 to the side walls 2 he inserts a solid object 27 into the interior attaching it to the base 3 by screws 28. This object will be of slightly smaller diameter than the inside diameter of the vessel 1, and a slot is cut at right angles to the face to accept the piston-and-cylinder device 11 with clearance. The thickness of object 27 should be such that it leaves a clearance between the top of the object and the underside of the lapping surface 9. Inlet 4 must be positioned so as to allow fluid admitted through it to reach the piston-and-cylinder device 11 and the underside of the lapping surface. Object 27 and base 3 could alternatively be made as one.

When the vessel leaves the maker face 10 is accurately shaped. Before use, filler plug 5 is removed, and knob 26 is turned so that piston 18 is at the rear end of its stroke (i.e. in its uppermost position as seen in FIG. 2). The device is laid with face 10 downmost, and filled with hydraulic fluid or other suitable pressure medium through inlet 4 until just full. Plug 5 is now replaced, the device is turned the other way up, and face 10 of surface 9 is used as the lapping surface. After some use, face 10 wears concave. Knob 26 is now turned so that piston 18 descends a little in cylinder 14. This of course tends to alter the effective volume available for fluid within vessel 1, and since the previous volume was full of fluid the vessel walls have to give. Surface 9, being the most flexible, gives first and bulges outwards, thus counteracting the concavity. Face 10 may be checked by known means to determine when the movement of piston 18 has restored it as near to the desired shape as is possible, and perfect shape may then be achieved by slight re-lapping which will take far less long and remove far less surface than would have been necessary otherwise.

It will be appreciated that base 3 can be provided in known manner with more than one orifice like inlet 4, in order to facilitate bleeding when the vessel is filled.

Since face 10 will generally tend to wear concave, it is'also possible that this surface could initially be of plano-convex shape, i.e. thicker at the middle than at the edges, with the convex face innermost. It will also be apparent that the shape of face 10 must correspond closely to the desired shape of the finished work but need not be exactly the same. For instance, the technique of some operators may produce a truly flat surface on the work most easily if face 10 is slightly convex. It is also clearly possible that face 10 could be made more strongly convex, or concave, to produce work of corresponding non-flat shape.

In a device as shown in the drawings a fluid pressure of a few p.s.i. is all that is required in normal use.

I claim:

1. A lapping device, comprising:

flexible wall means having a lapping surface defined exteriorly thereon;

a rigid-walled pressure vessel having an internal,

sealed cavity for containing pressurized incompressible fluid;

the flexible wall means being mounted externally on the pressure vessel with the opposite side of said wall means from said lapping surface in such communication with said internal cavity as to distend outwardly upon the increase of pressure with said cavity;

an adjustment means mounted on said pressure vessel in communication with said internal cavity for adjustable intrusion into said cavity to increase and decrease the volume of said cavity;

whereby when the cavity is filled with incompressible fluid and the lapping surface has become deviated from the desired spatial configuration thereof, for at least a narrow range of such deviation, the adjustment means may be actuated in a sense to cause the fluid to bulge the flexible wall to an extent necessary to reconfigure the lapping surface to the desired spatial configuration thereof.

2. The lapping device of claim 1 wherein the cavity is filled with incompressible fluid.

3. The lapping device of claim 2, wherein:

surface has a nominally flat spatial configuration.

5. The lapping device of claim 2 wherein the flexible wall means includes a flexible membrane integrally formed with at least part of said rigid-walled pressure vessel, said lapping surface being exteriorly provided on said flexible membrane. 

1. A lapping device, comprising: flexible wall means having a lapping surface defined exteriorly thereon; a rigid-walled pressure vessel having an internal, sealed cavity for containing pressurized incompressible fluid; the flexible wall means being mounted externally on the pressure vessel with the opposite side of said wall means from said lapping surface in such communication with said internal cavity as to distend outwardly upon the increase of pressure with said cavity; an adjustment means mounted on said pressure vessel in communication with said internal cavity for adjustable intrusion into said cavity to increase and decrease the volume of said cavity; whereby when the cavity is filled with incompressible fluid and the lapping surface has become deviated from the desired spatial configuration thereof, for at least a narrow range of such deviation, the adjustment means may be actuated in a sense to cause the fluid to bulge the flexible wall to an extent necessary to reconfigure the lapping surface to the desired spatial configuration thereof.
 2. The lapping device of claim 1 wherein the cavity is filled with incompressible fluid.
 3. The lapping device of claim 2, wherein: the adjustment means is provided by threaded opening means through the rigid-walled pressure vessel into said cavity and complementarily threaded screw means threadably received in the threaded opening means whereby further intrusion of the screw means into the cavity decreases the volume of the cavity.
 4. The lapping device of claim 2 wherein the lapping surface has a nominally flat spatial configuration.
 5. The lapping device of claim 2 wherein the flexible wall means includes a flexible membrane integrally formed with at least part of said rigid-walled pressure vessel, said lapping surface being exteriorly provided on said flexible membrane. 